Bioprinting 101: Part 6 – Pluronics

We are going to discuss pluronics today. We have covered a couple different materials within our bioprinting series. We will today discuss in this article the different material properties of a pluronic, what the typical usage for a pluronic is outside of bioprinting, and why we use pluronics within the bioprinting industry. So sit back and get ready for something fun and informative.

Pluronics or poloxamers are tri-block copolymers of poly(ethylene oxide) poly(propylene oxide)-poly(ethylene oxide). This group of synthetic polymers is thermoreversible in aqueous solutions. The ability to be thermoreversible refers to a property of certain substances to be reversed when exposed to heat.

Such thermoreversible substances can form a gel when cooled and return to a viscous fluid state when exposed to heat. The hydrophilic ethylene oxide and the hydrophobic propylene oxide give pluronics an amphiphilic structure – meaning it has a polar, water-soluble group attached to a nonpolar water-insoluble hydrocarbon chain.

Amphiphilic properties allow a material to love water as well as fats. This makes a material that is easy to bond with others in different gel phases. This is why amphiphilic properties are essential within biochemistry because of the way the body works. It is a system that is typically in transit and it needs to be multidimensional in terms of interactions within our body. Soap is a typical pluronic due to its ability to clean surfaces no matter what type of substance is on a surface (oil, liquid, food, etc.).

So what benefits may be derived from using pluronics within bioprinting? There is a particular pluronic of interest to bioprinting. This pluronic is F-127. F-127 is often used in tissue engineering because of the commercial availability of a consistent product that will undergo a sol-gel transition near physiological temperature and pH.

Pluronics are known to inhibit surface–tissue adhesion for many cell types, they have been successfully used for scaffolding applications that involve hematopoietic stem cells and lung tissue. Hematopoietic stem cells refer to an immature cell that can develop into all types of blood cells, including white blood cells, red blood cells, and platelets. Hematopoietic stem cells are found in the peripheral blood and the bone marrow.

A disadvantage of pluronics are fast degradation rate in vivo. In vivo refers to any process that is occuring within a live organism. Thus one can see how problems arise when trying to use pluronics in a setting such as the body. To overcome this problem, a pluronic is crosslinked with another α-hydroxy or amino acid in order to alter the chemical structure of its depsipeptide unit.

A depsipeptide is a peptide in which one or more of its amide groups are replaced by the corresponding ester. Many depsipeptides have both peptide and ester linkages. They are mainly found in marine and microbial natural products.

Pluronics are used extensively in rapid prototyping settings due to their properties. This material is best for rapid prototyping as it can be reversible thermally. It also is not the best in vivo. This causes it to be a good resource for prototyping, but not necessarily the best material for creating materials that will go into the body.

We have discussed a variety of biomaterials thus far in this series. This series is focusing on giving people some insight into the bioprinting industry as well as biomaterials as a whole. We have talked about hydrogels, alginate, and pluronics thus far. In the system of biology it is vital to have multiple options due to the complexity of things such as the human body. It is important to use these materials in combination due to no material being perfect. These are only a couple of biomaterials. We have just begun our exploration of bioprinting and biomaterials.